Wireless communication systems are widely used to provide voice and data services for multiple users using a variety of access terminals such as cellular telephones, laptop computers and various multimedia devices. Such communications systems can encompass local area networks, such as IEEE 801.11 networks, cellular telephone and/or mobile broadband networks. The communication system can use a one or more multiple access techniques, such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA) and others. Mobile broadband networks can conform to a number of system types or partnerships such as, General Packet Radio Service (GPRS), 3rd-Generation standards (3G), Worldwide Interoperability for Microwave Access (WiMAX), Universal Mobile Telecommunications System (UMTS), the 3rd Generation Partnership Project (3GPP), Evolution-Data Optimized EV-DO, or Long Term Evolution (LTE).
In wireless communication systems, the desired signal level as well as the interference level fluctuates in time due to temporal fading. In systems where multiple users share the same time slot or frequency bandwidth, highest performance is achieved when transmissions occur when the desired signal level is high and the interference level is low. This happens as naturally in downlink transmissions for some systems, such as LTE that are configured to have a user terminal transmit a latest carrier to interference ratio (C/I) value to the base station. In noise limited systems, the C/I value is highest when the desired signal is at the highest level and the interference is at the lowest level.
When a base station selects a user device independently, the interference from all adjacent cells changes during every transmission time interval (TTI). Interference, therefore, fluctuates rapidly. Even if the base station can predict the amplitude of the desired signal from a user device, the fast changing interference environment makes it very difficult for the base station to determine an appropriate modulation and coding selection (MCS) during the link adaptation process. The base station, therefore, will use a considerable fade margin to minimize transmission errors at the cost of lower data rates and system capacity.